Using Global Position System (GPS) satellite navigation is commonplace in modern vehicles. A GPS receiver in a vehicle can determine its position on the globe by receiving signals from at least four satellites whose positions are known with great precision. Based on these signals, the GPS receiver triangulates the vehicle position. Entities who wish to subvert a vehicle's navigation system can transmit spurious counterfeit GPS signals. If these spurious signals are received by a GPS receiver, the GPS receiver will calculate and report an incorrect position. Sending out counterfeit GPS signals is referred to as “GPS spoofing,” and is becoming increasingly problematic, particularly in the field of aviation.
The existing solutions for detecting GPS spoofing include satellite signal encryption/authentication. Because this method requires Global Navigation Satellite System (GNSS) civil signal redesign, it could be costly and carries a potentially huge impact on existing GPS users. Another solution is statistical tests of GPS signal measurements including code measurement, carrier phase, signal power, and Doppler frequency. This method is subject to false alarms and missed detection due to normal signal variation and multipath environments. Also these GPS signal measurement data normally are not available at GPS receiver outputs. Another solution is a position consistency check with other position sensors, e.g., inertial reference system (IRS), radio positions based on distance measurement equipment (DME/DME) or very high frequency omnidirectional ranging (DME/VOR). This could be unreliable because of inherent IRS drift and the radio position is not always available.